Project Summary/Abstract Optogenetics encompasses a broad array of tools and techniques that involve the use of light, in conjunction with molecular genetic tools, to drive and monitor activity of specific types of excitable cells in the nervous system and heart. Compared to traditional electrophysiological techniques, these methods are far less invasive and have the potential to monitor and manipulate electrical activity at multiple sites at the same time. The promise of optogenetics is not solely limited to expanding our basic understanding of complex organ systems but will also have a profound impact on the development of new therapeutics. Despite their promise, the current generation of optogenetic actuators are inferior compared to standard electrophysiological methods. While the membrane potential in a typical electrophysiological experiment can be changed by hundreds of millivolts on a sub- millisecond timescale, the current generation of light-activated ion channels are able to drive membrane potential by only a few millivolts in a millisecond. Much of the cutting-edge development in the field has focused on modifying and reengineering naturally-occurring ion channels, but these approaches have some inherent limitations. Herein, we propose to develop a new class of synthetic probes that serve as light-activated actuators for controlling membrane potential and ion concentrations with high temporal and spatial resolution. Employing a chemical synthesis approach towards these probes will allow us much greater flexibility to engineer and design more efficient actuators having the necessary throughput to drive cellular membrane potential. In addition, these chemical ion carriers can be combined with genetically encoded light-activated probes to provide even greater flexibility. The proposed research capitalizes on the expertise of a synthetic chemist (Prof. Schomaker, UW- Chemistry) and an ion channel electrophysiologist (Prof. Chanda, UW-Neuroscience). The two specific aims will focus on: a) the design and synthesis of photoactive ionophores and ion carriers, b) Characterization of the optical and transport properties of these designer ionophores and ion carriers.